Kemal Kilicdaroglu, leader of Turkey's main opposition Republican People's Party (CHP), talks to media after visiting his party's lawmaker Enis Berberoglu at Maltepe prison, in Istanbul, Turkey on July 10, 2017. Umit Bektas/Reuters

ISTANBUL // Turkey issued arrest warrants for 72 university staff, state media said on Monday, including a former adviser to the main opposition leader who staged a mass rally on Sunday to protest a crackdown since a failed military coup last year.

The warrants were issued under an investigation into the movement of the US-based Islamic cleric Fethullah Gulen, who is accused of orchestrating the failed coup to oust President Recep Tayyip Erdogan on July 15, state-run Anadolu news agency reported. Mr Gulen strongly denies the charges.

Kemal Kilicdaroglu, leader of the secularist People's Republican Party (CHP), told a huge crowd on Sunday that Turkey was living under dictatorship and pledged to keep challenging the government after completing a 25-day protest march from Ankara to Istanbul.

Police have so far detained 42 of the staff from Istanbul's prestigious Bogazici University and Medeniyet University, which is based on the Asian side of the country's largest city, Anadolu said.

It said eight of the 72 were from Bogazici, including well-known academic Koray Caliskan, who worked in the past as a voluntary adviser to Mr Kilicdaroglu, CHP lawmaker Oguz Kaan Salici said on Twitter.

The other 64 people being detained were from Medeniyet University, 19 of whom were medical faculty professors, Anadolu said. All were suspected users of ByLock, an encrypted messaging app the government says was used by Mr Gulen's followers.

About 50,000 people have been arrested and 150,000 state workers including teachers, judges and soldiers, have been suspended in the crackdown under emergency rule which was imposed soon after the attempted military takeover.

Although activists and western governments have criticised the crackdown, the government insists it is necessary to tackle the security threat they say is posed by the Gulen movement.

Mr Kilicdaroglu launched his 450km march after fellow MP Enis Berberoglu became the first CHP lawmaker jailed in the purge, sentenced to 25 years in jail on spying charges.

Rights groups and government critics say Turkey has been drifting toward authoritarianism for years, a process they say accelerated since the coup bid and a referendum in April granting president Recep Tayyip Erdogan sweeping new powers.